An image sensor is a semiconductor device that converts an optical image into an electrical signal. The image sensor can be classified as a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor (CIS).
A unit pixel of a CIS includes a photodiode and a metal oxide semiconductor (MOS) transistor. Therefore, the CIS sequentially detects an electrical signal of the unit pixel in a switching manner to generate an image.
Although efforts are being made to increase the fill factor of the image sensor for improving optical sensitivity, there is a limitation in increasing the fill factor because of the logic circuitry region in a pixel area.
To improve the optical sensitivity, a method of forming a microlens has been developed, which concentrates incident light out of a light-sensing region onto the light-sensing region.
The microlens is typically formed on a pixel array substrate according to pixels. Often, the microlens is formed on a color filter.
The microlens is formed in a dome shape by sequentially performing exposure, development, and reflow processes on a photosensitive organic material.
However, since the photosensitive organic material has a weak physical property, the microlens is susceptible to cracking from physical impact during subsequent package and bump processes. Also, the photosensitive organic material has relatively strong viscosity and may generate a defective microlens due to the adsorption of particles.